def maraphon(a):   
    if a==1: return False   
    test=True   
    k=a-1   
    while k>1:   
        if not a%k:   
            test=False               
            break   
        k -= 1       
    return test  
     
n=input() 
g=[] 
for i in range(len(n) + 1): 
    for k in range(i,len(n) + 1): 
        if i==k: 
            continue 
        a=int(n[i:k]) 
        if  maraphon(a): 
            g += [a] 
print(max(g) if g else 0)
